To easily perform a hill-start of a vehicle with a manual transmission mounted thereon by utilizing a differential device.

A sleeve 31 to be spline-coupled with an outer circumference of an extension shaft 22 of a differential device D has first spline teeth 31b to be engaged with spline teeth 15a of a differential case 15, and second spline teeth 13c to be engaged with spline teeth 13a of a housing 13. When the position of the sleeve 31 is in a supporting condition of the start on slope shown in the figure, the spline teeth 31b, 31c, 15a and 13a are engaged with each other, and the extension shaft 22 and a right axle 26R are constrained in a non-rotational manner. Therefore, a vehicle can be stopped on a slope without actuating a parking brake, and can perform a smooth hill-start by freeing constraint of the extension shaft 22 and the right axle 26R by moving the sleeve 31 to the left by an actuator as the vehicle starts.